Hybrid lift pin

ABSTRACT

A lift pin and a substrate support assembly and reactor including the lift pin are disclosed. The lift pin includes first section comprising a material having a first transparency and a second section comprising a material having a second transparency. The lift pin can provide improved temperature uniformity across substrate support assembly including the lift pin during substrate processing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/621,820, entitled “HYBRID LIFT PIN” and filed on Jan. 25, 2018, the disclosure of which is hereby incorporated herein for reference.

FIELD OF INVENTION

The disclosure generally relates to apparatus for gas-phase processes. More particularly, exemplary embodiments of the present disclosure relate to lift pins and to apparatus including lift pins.

BACKGROUND OF THE DISCLOSURE

Gas-phase reactors for processing substrates, such as semiconductor wafers, often include a susceptor within a reaction chamber. During processing, one or more substrates are placed within the reaction chamber and onto the susceptor using a robotic arm. After processing, the substrate(s) are removed from the surface of the susceptor and through an opening in the reaction chamber using the robotic arm.

During the substrate transfer process, lift pins, which extend through a vertical width of the susceptor and beyond, can be used to facilitate placement and removal of the substrate on and from the surface of the susceptor. In such cases, a substrate can be placed onto the susceptor by causing the lift pins to rise above the surface of the susceptor, placing the substrate onto the lift pins, and lowering the lift pins, such that the substrate rests on the susceptor.

The susceptor and the lift pins are often formed of different materials. For example, a susceptor can be formed of silicon carbide coated graphite, and lift pins can be formed of silicon carbide or quartz. Because of differences in emissivity, heat conductance, and/or heat capacity of the different susceptor and lift pin materials, hot or cold spots can form on a substrate overlying the susceptor in the locations of the lift pins. The hot or cold spots can cause deposition or etch rates of material on a surface of the substrate in the area of the lift pins to be different (higher or lower) than areas away from the lift pins.

Accordingly, improved lift pins and apparatus including the lift pins are desired.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure provide improved lift pins and apparatus including the lift pins. As set forth in more detail below, in accordance with various embodiments of the disclosure, the improved lift pins provide better temperature uniformity across a surface of a substrate support assembly including the improved lift pins.

In accordance with at least one embodiment of the disclosure, a lift pin includes a first section comprising a material having a first transparency and a second section comprising a material having a second transparency. The second section can act as a light pipe, collecting and reflecting all or most of the infrared and/or visible light and transmitting the infrared and/or visible light to the first section. In accordance with various aspects of these embodiments, the material having a first transparency comprises quartz. The material having a first transparency can be relatively opaque in the infrared region of the light spectrum—also referred to herein as infrared light (e.g., light having a wavelength of about 750 nm to about 1 mm), as measured, using e.g., Fourier-transform infrared spectroscopy (FTIR). For example, the first transparency of infrared light can range from 0 or about 0 to about 10%, 0 or about 0 to about 5%, or 0 or about 0 to about 2%. The material having a second transparency can additionally or alternatively comprises quartz. The second transparency of infrared light can range from about 85 to about 100%, about 90 to about 100% (or less than 100%), or about 95 to about 100% (or less than 100%). In accordance with further aspects, the lift pin can include about 1 to about 60%, about 2 to about 55%, or about 5 to about 50% of the first section by length, mass, or volume. Additionally or alternatively, the lift pin can include about 40 to about 99%, about 2 to about 98%, or about 45 to about 98% of the second section by length, mass, or volume. The first section and the second section can be fused or welded together to form the lift pin.

In accordance with further exemplary embodiments of the disclosure, a substrate support assembly includes a susceptor and one or more lift pins, such as a lift pin as described herein. The substrate support assembly can additionally include a susceptor support coupled to the susceptor, a rotatable shaft coupled to the susceptor support, and a lift pin mechanism to cause the moveable shaft to move in a vertical direction during a substrate transfer process. The substrate support assembly can also include a susceptor rotation mechanism that causes the susceptor to rotate during substrate processing. In accordance with exemplary aspects of the disclosure, the susceptor support includes a plurality of susceptor support arms and one or more susceptor support structures coupled to or integrated with each of the plurality of support arms. In accordance with yet further aspects, at least one of the plurality of susceptor support arms comprises an aperture to receive one of the one or more lift pins. Further, the susceptor can include a center region and a peripheral region, wherein a width of the center region is greater than a width of the peripheral region.

In accordance with additional embodiments of the disclosure, a reactor includes one or more lift pins as described herein.

And, in accordance with yet further exemplary embodiments, a reactor includes a substrate support assembly as described herein.

Both the foregoing summary and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure or the claimed invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A more complete understanding of the embodiments of the present disclosure may be derived by referring to the detailed description and claims when considered in connection with the following illustrative figures.

FIGS. 1-4 illustrate lift pins in accordance with various exemplary embodiments of the disclosure.

FIG. 5 illustrates a cross-sectional view of a lift pin in accordance with exemplary embodiments of the disclosure.

FIG. 6 illustrates an exploded view of a lift pin in accordance with exemplary embodiments of the disclosure.

FIG. 7 illustrates a cross-sectional view of a substrate support assembly in accordance with exemplary embodiments of the disclosure.

FIG. 8 illustrates a bottom perspective view of the substrate support assembly in accordance with exemplary embodiments of the disclosure.

FIG. 9 illustrates normalized thickness variation across a surface of a substrate at various temperatures.

FIG. 10 illustrates normalized thickness of a film using various lift pin materials.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present disclosure generally relates to lift pins and assemblies including the lift pins. As set forth in more detail below, the lift pins and the assemblies can be used in the manufacturing of devices, such as devices formed using semiconductor substrates.

The description of exemplary embodiments of lift pins and assemblies provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the disclosure or the claims. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.

The lift pins and assemblies described herein can be used to mitigate temperature variation across a surface of the substrate support assembly (e.g., across a surface of a susceptor of the assembly) and/or across a surface of a substrate. By reducing temperature variation across the susceptor and/or substrate surface, more uniform processing (e.g., cleaning, depositing, or etching of material) across a surface of the substrate can be achieved.

Turning now to FIGS. 1-4, lift pins 100, 200, 300 and 400 are illustrated. Lift pin 100 includes a first section 102 and a second section 104. Lift pin 200 includes a first section 202 and a second section 204. Lift pin 300 includes a first section 302 and a second section 304. Lift pin 400 includes a first section 402 and a second section 404.

Each first section 102, 202, 302 and 402 can include a material having a first transparency in the infrared region. The material having a first transparency can be or comprise, for example, quartz, such as opaque quartz. The first transparency can range from 0 or about 0 to about 10%), 0 or about 0 to about 5%, or 0 or about 0 to about 2% infrared light transmission. By way of particular example, the material having a first transparency can be or include quartz material available from Heraeus under the name Opaque Materials [OM] 100.

Similarly, each second section 104, 204, 304 and 404 can include a material having a second transparency in the infrared region. The material having a second transparency can be or comprise, for example, quartz, such as clear or transparent quartz. The second transparency can range from about 85 to about 100%, about 90 to about 100% (or less than 100%), or about 95 to about 100% (or less than 100%) transmission of infrared light. By way of particular example, the material having a second transparency can be or include fused quartz material available from Momentive under the name GE type 214 fused quartz.

In accordance with at least some exemplary embodiments, second sections 104, 204, 304 and 404 can act as a light pipe, collecting and reflecting all or most of the infrared and/or visible light and/or heat and transmitting the infrared and/or visible light/heat to the respective first section 102, 202, 302, 402. In this way, second section 104, 204, 304 and 404 can be used to facilitate heating of respective first section 102, 202, 302 and 402 by collecting light/heat from surrounding areas (e.g., from sections of a substrate support assembly) and transmitting the light/heat to the respective first sections to thereby mitigate temperature differentials that would otherwise be present on a surface of the substrate support assembly.

As illustrated in FIGS. 1-4, each lift pin 100, 200, 300, 400 can include a head 106, 206, 306, 406 and a body 108, 208, 308, 408. Each head 106, 206, 306, 406 can include a respective tapered portion 110, 210, 310, 410; a cylindrical portion 112, 212, 312, 412; and a top portion 114, 214, 314, 414.

Tapered portion 110, 210, 310, 410 can be or comprise a frusto-conical shape as illustrated. An angle of a side of tapered portion 110, 210, 310, 410 can range from about 30 to about 60 or be about 45 degrees relative to a vertical axis of the respective lift pin 100, 200, 300, 400.

Cylindrical portion 112, 212, 312, 412 can be or comprise a solid cylinder. As illustrated, cylindrical portion 112, 212, 312, 412 can be interposed between tapered portion 110, 210, 310, 410 and top portion 114, 214, 314, 414. A radius of cylindrical portion 112, 212, 312, 412 can range from about 3 mm to about 5 mm or be about 4 mm.

Top portion 114, 214, 314, 414 can be or include a flat surface. Alternatively, top portion 114, 214, 314, 414 can be domed with a radius of, for example, 1/20 to ⅕ or about 1/10 the radius of cylindrical portion 112, 212, 312, 412.

Each body 108, 208, 308, 408 can include or be a cylindrical shape. A bottom 116, 216, 316, 416 of respective body 104, 204, 304, 404 can be flat or include a rounded surface-e.g., having a domed shape with a radius of, for example, 1/20 to ⅕ or about 1/10 the radius of body 104, 204, 304, 404. A radius of body 104, 204, 304, 404 can range from about 2 mm to about 4 mm or be about 3 mm.

In accordance with some exemplary embodiments of the disclosure, head 106, 206, 306, 406, or a portion thereof, comprises first section 102, or a portion thereof, comprising the material having a first transparency. For example, as illustrated in FIG. 1, a portion of head 106 includes first section 102 comprising the material having a first transparency. In this illustrated example, head 106 also includes part of second section 102 comprising the material having a second transparency. With reference to FIGS. 2-4, lift pin 200, 300, 400 each include a respective first section 202, 302, 402, which includes head 206, 306, 406 and a portion of body 208, 308, 408.

FIGS. 5 and 6 illustrate an exemplary technique to fuse or weld together a first section 502 and a second section 504 of a lift pin 500. First section 502 and second section 504 can be the same or similar to first sections and second sections described above and particularly first section 202, 302 and 402 and second section 204, 304 and 404. Lift pin 500 can include a head 506 and a body 508, which can be the same or similar to the heads and bodies described above in connection with FIGS. 1-4.

To facilitate the coupling together of first section 502 and second section 504, one or more of first section 502 and second section 504 can include a coupling element 510 and the other of first section 502 and second section 504 can include a recess 512 to receive coupling element 510. In the illustrative example, coupling element 510 includes a first part 514, having a first length and a first diameter, and a second part 516, having a second length and a second diameter, wherein the first diameter is different (e.g., smaller) than the second diameter. The first and second lengths can be the same, similar, or different from one another.

In the illustrated example, second section 504 comprises two sections 506 and 508. Sections 506 and 508 can be coupled together (e.g., fused or welded) and to first section 502 to form lift pin 500.

Turning now to FIG. 7, a reactor 700 in accordance with at least one embodiment of the disclosure is illustrated. Reactor 700 includes a reaction chamber 702, including a reaction region 704 and a substrate lift mechanism 706. As described in more detail below, during a substrate transfer operation, substrate lift mechanism 706 facilitates placement of a substrate 716 onto a top surface 722 of a susceptor 718 within reaction region 704 to allow removal of substrate 716 through an opening 720 of reaction chamber 702.

Reaction chamber 702 can be formed of, for example, quartz, and can be formed as a unitary piece, such as a tube. By way of example, reaction region 704 within reaction chamber 702 can have a rectangular cross section having a width of about 350 mm to about 450 mm (or be about 420 mm), a length of about 400 mm to about 800 mm (or be about 760 mm), and a height of about 20 mm to about 40 mm (or be about 30 mm). As noted above, reaction chamber 702 includes an opening 720 that resides above top surface 722 of susceptor 718 (e.g., when surface 722 is in a processing position).

Reaction chamber 702 can be suitable for a variety of applications, such as film (e.g., epitaxial) deposition processes, etch processes, clean processes, and the like. Further, reactor 700 can be a standalone reactor or form part of a cluster tool that may include similar or different reaction chambers.

Substrate lift mechanism 706 includes at least one lift pin 708, 710 (e.g., any of the lift pins described above), a lift pin support member 712 that can engage with and couple to the at least one pin 708, 710, and a movable shaft 714 mechanically coupled to the lift pin support member. During a substrate transfer process, substrate lift mechanism 706 causes the at least one lift pin 708, 710 to be raised or lowered to allow placement of substrate 716 onto surface 722 and/or removal of substrate 716 from surface 722.

Although two lift pins 708, 710 are shown in FIG. 7, reactor 700 includes three (e.g., equally) spaced apart lift pins. Reactors in accordance with other embodiments of the disclosure can include any suitable number of lift pins and generally include three or more lift pins. A length L of lift pins 708, 710 can vary according to application. Generally a length of lift pins 708, 710 allows lift pins 708, 710 to extend through a width W of susceptor 718 and above the susceptor top surface 722—for example, when receiving a substrate 716 from a robotic arm (not illustrated) or presenting substrate 716 to be received by the robotic arm.

In accordance with some embodiments of the disclosure, lift pins 708, 710 have a length L of about 20 to about 40 mm or about 30 mm (e.g., about 32.3 mm). This is a significantly shorter length than typical lift pins and allows processing and substrate transfer within a common region, namely reaction region 704. Lift pins 708, 710 can include a beveled section 724 (e.g., tapered section as described above) that is received within a portion of susceptor 718. Beveled section 724 allows lift pins 708, 710 to be received within a via 726 within susceptor 718 and to be retained at a desired level (e.g., a top surface of lift pins can be about planar with surface 722 or reside just (e.g., a few mm or less) below surface 722. This allows susceptor 718 to retain lift pins 708, 710 when, for example, lift pin support member 712 is not engaged with lift pins 708, 710. A top surface 728, 730 of lift pins 708, 710 can have a diameter of about 3 to about 6 mm, or about 4 mm, as noted above. Top surface 728, 730 can be polished to a smooth finish (e.g., a roughness average of about 0.05 to 0.2 μm or less) to prevent or mitigate surface damage to substrate 716 during a transfer process.

Lift pin support member 712 engages with lift pins 708, 710 and moveable shaft 714. In the illustrated example, lift pin support member 712 removably engages with lift pins 708, 710 and is coupled to moveable shaft 714. This allows movable shaft 714 to move only in a vertical direction (and not rotate), while allowing susceptor 718 to rotate—e.g., during substrate processing. Lift pin support member 712 can be formed of, for example, SiC-coated graphite, quartz, or glassy carbon.

As illustrated in more detail in FIG. 8, lift pin support member 712 includes a plurality of lift pin arms 802, 804. Although two lift pin support arms are illustrated in FIG. 8, the illustrated lift pin support member 712 includes three lift pin support arms. Each lift pin support arm 802, 804 includes a first end 806, 808 coupled to moveable shaft 714 and a second end 810, 812 that receives and engages with a lift pin (e.g., one of lift pins 708, 710). Second end 810, 812 can include, for example, a recess 814, 816 to receive a bottom portion 818, 820 of one or more lift pins 708, 710. Lift pin support member 712 can be a unitary member, as illustrated. Alternatively, lift pin support member 712 can include a plurality of arms coupled to a coupling that is coupled to moveable shaft 714.

FIG. 7 illustrates lift pins 708, 710 when engaged with lift pin support member 712, such that lift pin support member 712 engages with lift pins 708, 710 and causes top surface 728, 730 of lift pins 708, 710 to reside above surface 722. FIG. 8 illustrates lift pin support member 712, when lift pin support member 712 is disengaged from lift pins 708, 710—i.e., when moveable shaft 714 is moved in a downward position relative to the position of moveable shaft 714 in FIG. 7. As illustrated in FIG. 8, when lift pin support member 712 is disengaged from lift pins 708, 710, lift pins 708, 710 are retained by susceptor 718, allowing susceptor 718 to rotate, without requiring support member 712 and/or moveable shaft 714 to rotate.

Moveable shaft 714 is in the form of a hollow tube. Moveable shaft 714 can be formed of, for example, quartz. In accordance with exemplary embodiments of the disclosure, moveable shaft is configured to move a vertical distance of 5 to about 25 mm (or ˜17 mm). As a result, lift pins 708, 710 can move about 5 to about 25 mm (or ˜17 mm), and lift pins 708, 710 can extend to a height of up to about 5, 10, or 20 mm above surface 722.

Susceptor 718 can be formed of, for example, SiC or SiC-coated graphite. In accordance with various examples of the disclosure, width W of susceptor 718 is relatively small to allow lift pin-assisted substrate transfer and processing in a single region—e.g., reaction region 704. In accordance with various embodiments of the disclosure, a width W of susceptor 718 at a peripheral region 822 is less than a width of susceptor 718 at a center region 824 of susceptor 718. This configuration can allow for a relatively thin susceptor—especially at the peripheral region—while allowing susceptor 718 to rotate and perform other functions, such as protecting an end of a thermocouple and providing desired heat transfer to and/or from substrate 716. By way of examples, the width at peripheral region 822 ranges from about 3 to about 6.5 mm (or be ˜3.8 mm). A width of center region 824 can range from about 6 to about 10 mm (or be ˜6.4 mm).

As noted above, reactor 700 can be configured to cause substrate 716 to rotate during substrate processing. In this illustrated example, reactor 700 includes a rotatable shaft 732 and a susceptor support 734 to cause susceptor 718, and consequently substrate 716, to rotate during processing.

Rotatable shaft 732 can be formed of, for example, quartz. Rotatable shaft 732 can be configured to couple to susceptor support 734 to translate rotational movement of rotatable shaft 732 to susceptor support 734. By way of example, rotatable shaft 732 can be coupled to susceptor support 734 using a coupling 748.

As illustrated in FIGS. 7 and 8, susceptor support 734 includes one or more (e.g., a plurality of) susceptor support arms 826, 828 and structures 736, 738. Structures 736, 738 can engage with susceptor 718 and susceptor support arms 826, 828. Alternatively, structures 736, 738 can be integrally formed with susceptor support arms 826, 828. Susceptor support arms 826, 828 and structures 736, 738 can be formed of, for example, SiC, SiC-coated graphite, or quartz. Although illustrated with one structure 736, 738 for each susceptor support arms 826, 828, susceptor support 734 can include a plurality of structures 736, 738 for each susceptor support arm 826, 828. In accordance with exemplary embodiments of the disclosure, at least one of the plurality of susceptor support arms 826, 828 includes an aperture 740, 742 to receive a lift pin.

Reactor 700 can also include a thermocouple 744. Thermocouple 744 can be used to measure a temperature of susceptor 718—for example—during substrate processing. As illustrated in FIG. 7, thermocouple 744 can include an end 746, which extends through moveable shaft 714 and rotatable shaft 732. End 746 can reside within center region 824 of susceptor 718. Center region 824 may provide additional radiation shielding for end 746 of thermocouple 744.

In accordance with further exemplary embodiments of the disclosure, a substrate support assembly 830 includes components to cause lift pins 708, 710 to raise and lower and to cause susceptor 718 to rotate. In accordance with these embodiments, substrate support assembly 830 includes susceptor 718, susceptor support 734, rotatable shaft 732, lift pin support member 712, one or more lift pins 708, 710, moveable shaft 714, a lift pin mechanism to cause the moveable shaft to move in a vertical direction during a substrate transfer process, and a susceptor rotation mechanism that causes susceptor 718 to rotate during substrate processing. As noted above, in accordance with various examples of the disclosure, susceptor 718 does not move in a vertical direction during substrate transfer—i.e., susceptor 718 does not move in a vertical direction as lift pins are raised and/or lowered and/or during other steps of a substrate transfer process. The lift pin mechanism and the susceptor rotation mechanism can be combined, as described in U.S. application Ser. No. 15/672,096, entitled SUBSTRATE LIFT MECHANISM AND REACTOR INCLUDING SAME, filed Aug. 8, 2017, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

FIG. 9 illustrates normalized thickness of a 100.37 mm radius, high density pin defect scan at various substrate bias temperatures. The scans were run with a lift pin comprising opaque material. As illustrated, a thickness of a deposited film decreases significantly in an area about a lift pin.

FIG. 10 illustrates a radial thickness scan of a substrate processed with a clear quartz lift pin, a silicon carbide (SiC) lift pin, and an opaque quartz pin. As illustrated, each of the various types of lift pins causes either an increase or a decrease in an amount of material deposited onto a substrate. The lift pins, assemblies and reactors described herein can mitigate or eliminate these deviations.

In accordance with additional embodiments of the disclosure, a method of transferring and processing a substrate is provided. The method can employ the reactor, substrate support assembly, and/or lift pin as described herein. An exemplary method includes the steps of providing a reactor comprising a common region for substrate processing and substrate transfer, providing a substrate support assembly, providing a substrate to the common region, moving the lift pins in a downward position to place the substrate in a processing position, processing the substrate, moving the lift pins in an upward position, and removing the substrate from the common region. The step of removing the substrate can include removing the substrate from the common region through an opening in a reaction or processing region that is above a top surface of the susceptor.

Although exemplary embodiments of the present disclosure are set forth herein, it should be appreciated that the disclosure is not so limited. For example, although the system and method are described in connection with various specific materials, the disclosure is not necessarily limited to these materials. Various modifications, variations, and enhancements of the lift pins, assemblies, and methods set forth herein may be made without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A lift pin comprising: a first section comprising a material having a first transparency to infrared light; and a second section comprising a material having a second transparency to infrared light.
 2. The lift pin of claim 1, wherein the material having a first transparency comprises quartz.
 3. The lift pin of claim 1, wherein the first transparency ranges from 0 or about 0 to about 10% transmission of infrared light.
 4. The lift pin of claim 1, wherein the first transparency ranges from 0 or about 0 to about 5% transmission of infrared light.
 5. The lift pin of claim 1, wherein the first transparency ranges from 0 or about 0 to about 2% transmission of infrared light.
 6. The lift pin of claim 1, wherein the material having a second transparency comprises quartz.
 7. The lift pin of claim 1, wherein the second transparency ranges from about 85% to about 100% transmission of infrared light.
 8. The lift pin of claim 1, wherein the second transparency ranges from about 90% to less than 100% transmission of infrared light.
 9. The lift pin of claim 1, wherein the lift pin comprises about 2% to about 55% by length of the first section.
 10. The lift pin of claim 1, wherein the lift pin comprises about 45% to about 98% by length of the second section.
 11. The lift pin of claim 1, wherein the first section and the second section are fused together.
 12. The lift pin of claim 1, wherein the first section comprises a body and a head, wherein a cross-sectional dimension of the head is greater than a cross-sectional dimension of the body.
 13. The lift pin of claim 1, wherein the second section is substantially cylindrical.
 14. A substrate support assembly comprising: a susceptor; a susceptor support coupled to the susceptor; a rotatable shaft coupled to the susceptor support; a lift pin support member; one or more lift pins according to claim 1 coupled to the lift pin support member; a moveable shaft coupled to the lift pin support member; a lift pin mechanism to cause the moveable shaft to move in a vertical direction during a substrate transfer process; and a susceptor rotation mechanism that causes the susceptor to rotate during substrate processing.
 15. The substrate support assembly of claim 14, wherein the susceptor support comprises a plurality of susceptor support arms and one or more susceptor support structures coupled to or integrated with each of the plurality of support arms.
 16. The substrate support assembly of claim 14, wherein at least one of the plurality of susceptor support arms comprises an aperture to receive one of the one or more lift pins.
 17. The substrate support assembly of any of claim 14, wherein the susceptor comprises a center region and a peripheral region and wherein a width of the center region is greater than a width of the peripheral region.
 18. The substrate support assembly of claim 14, comprising two or more of the lift pins.
 19. A reactor comprising one or more lift pins of claim
 1. 20. The reactor of claim 19, further comprising a susceptor configured to receive the one or more lift pins. 